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<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.karma.reference.directive.columns"></a><a class="link" href="columns.html" title="Generator Directive Separating Output Into Columns (columns[])">Generator
          Directive Separating Output Into Columns (<code class="computeroutput"><span class="identifier">columns</span><span class="special">[]</span></code>)</a>
</h5></div></div></div>
<h6>
<a name="spirit.karma.reference.directive.columns.h0"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.description"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.description">Description</a>
          </h6>
<p>
            The <code class="computeroutput"><span class="identifier">columns</span><span class="special">[]</span></code>
            directive separates the output emitted by the embedded generator by inserting
            special column separators.
          </p>
<h6>
<a name="spirit.karma.reference.directive.columns.h1"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.header"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.header">Header</a>
          </h6>
<pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/karma/directive/columns.hpp&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma_columns</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
            Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
                    <p>
                      Name
                    </p>
                  </th></tr></thead>
<tbody><tr><td>
                    <p>
                      <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">columns</span> <span class="comment">//
                      alias: boost::spirit::karma::columns</span></code>
                    </p>
                  </td></tr></tbody>
</table></div>
<h6>
<a name="spirit.karma.reference.directive.columns.h2"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.model_of"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.model_of">Model of</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>
            </p></blockquote></div>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt>
<dd><p>
                  A generator object
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">g</span></code></span></dt>
<dd><p>
                  A generator object, or a <a class="link" href="../basics.html#spirit.karma.reference.basics.lazy_argument">Lazy
                  Argument</a> that evaluates to a generator object, will be used
                  to emit column separators
                </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">A</span></code></span></dt>
<dd>
<p>
                  Attribute type of generator <code class="computeroutput"><span class="identifier">a</span></code>
                </p>
<p>
                  [<code class="computeroutput"><span class="identifier">num</span></code>
                </p>
<p>
                  Numeric literal, any unsigned integer value, or a <a class="link" href="../basics.html#spirit.karma.reference.basics.lazy_argument">Lazy
                  Argument</a> that evaluates to an unsigned integer value defining
                  the number of items to emit in between the column separators
                </p>
</dd>
</dl>
</div>
<h6>
<a name="spirit.karma.reference.directive.columns.h3"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.expression_semantics"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.expression_semantics">Expression
            Semantics</a>
          </h6>
<p>
            Semantics of an expression is defined only where it differs from, or
            is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The <code class="computeroutput"><span class="identifier">columns</span></code>
                      directive invokes a generator after each N-th element of the
                      embedded generator has been emitted. The number of columns
                      is defined by the preprocessor constant <code class="computeroutput"><span class="identifier">BOOST_KARMA_DEFAULT_COLUMNS</span></code>.
                      The column separator used will be <code class="computeroutput"><span class="identifier">karma</span><span class="special">::</span><span class="identifier">eol</span></code>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The <code class="computeroutput"><span class="identifier">columns</span></code>
                      directive invokes a generator after each N-th element of the
                      embedded generator has been emitted. The number of columns
                      is defined by the argument to the directive <code class="computeroutput"><span class="identifier">num</span></code>.
                      The column separator used will be <code class="computeroutput"><span class="identifier">karma</span><span class="special">::</span><span class="identifier">eol</span></code>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">(</span><span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The <code class="computeroutput"><span class="identifier">columns</span></code>
                      directive invokes a generator after each N-th element of the
                      embedded generator has been emitted. The number of columns
                      is defined by the preprocessor constant <code class="computeroutput"><span class="identifier">BOOST_KARMA_DEFAULT_COLUMNS</span></code>.
                      The column separator used will be <code class="computeroutput"><span class="identifier">g</span></code>.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span>
                      <span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The <code class="computeroutput"><span class="identifier">columns</span></code>
                      directive invokes a generator after each N-th element of the
                      embedded generator has been emitted. The number of columns
                      is defined by the argument to the directive <code class="computeroutput"><span class="identifier">num</span></code>.
                      The column separator used will be <code class="computeroutput"><span class="identifier">g</span></code>.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.karma.reference.directive.columns.h4"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.attributes"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.attributes">Attributes</a>
          </h6>
<p>
            See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound
            Attribute Notation</a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Attribute
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">(</span><span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">(</span><span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">(</span><span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span>
                      <span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]</span></code>
                    </p>
                  </td>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span> <span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">A</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="identifier">columns</span><span class="special">(</span><span class="identifier">num</span><span class="special">,</span> <span class="identifier">g</span><span class="special">)[</span><span class="identifier">a</span><span class="special">]:</span> <span class="identifier">Unused</span></pre>
<p>
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.karma.reference.directive.columns.h5"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.complexity"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.complexity">Complexity</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              The overall complexity of the <code class="computeroutput"><span class="identifier">columns</span></code>
              generator directive depends on the complexity of the embedded generator.
              The complexity of the <code class="computeroutput"><span class="identifier">columns</span></code>
              generator directive itself is O(N), where <code class="computeroutput"><span class="identifier">N</span></code>
              is the number of inserted column separators.
            </p></blockquote></div>
<h6>
<a name="spirit.karma.reference.directive.columns.h6"></a>
            <span class="phrase"><a name="spirit.karma.reference.directive.columns.example"></a></span><a class="link" href="columns.html#spirit.karma.reference.directive.columns.example">Example</a>
          </h6>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.karma.reference.basics.examples">Basics Examples</a>
              section.
            </p></td></tr>
</table></div>
<p>
            Some includes:
          </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="keyword">operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">proto</span><span class="special">/</span><span class="identifier">deep_copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span>
</pre>
<p>
          </p>
<p>
            Some using declarations:
          </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">columns</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">space</span><span class="special">;</span>
</pre>
<p>
          </p>
<p>
            Basic usage of the <code class="computeroutput"><span class="identifier">columns</span></code>
            generators:
          </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">v</span><span class="special">;</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1.0</span><span class="special">);</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">2.0</span><span class="special">);</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">3.0</span><span class="special">);</span>
<span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"1.0\n2.0\n3.0\n"</span><span class="special">,</span> <span class="identifier">columns</span><span class="special">(</span><span class="number">1</span><span class="special">)[*</span><span class="identifier">double_</span><span class="special">],</span> <span class="identifier">v</span><span class="special">);</span>
<span class="identifier">test_generator_attr_delim</span><span class="special">(</span><span class="string">"1.0 2.0 \n3.0 \n"</span><span class="special">,</span> <span class="identifier">columns</span><span class="special">(</span><span class="number">2</span><span class="special">)[*</span><span class="identifier">double_</span><span class="special">],</span> <span class="identifier">space</span><span class="special">,</span> <span class="identifier">v</span><span class="special">);</span>
</pre>
<p>
          </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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